Discriminator circuits



Patented Aug. 26, 1947 Donald D. Grieg,

Federal Telephone an Forest Hills, N. Y., assignor to d RadioCorporation, New

York, N. Y., acorporation of Delaware Application'S'eptember 11, 1944,Serial No. 553,569

7 Claims. 1

This invention relates to discriminator circuits and more particularlyto discriminator circuits serving as translators for time modulatedpulse trains.

Systems have been proposed for transmitting signals by means of pulsetrains wherein alternate pulses of the pulse-trains recur at asubstantially uniform repetition frequency and in which the time spacingbetween successive pulses is varied'in accordance with applied signals.The applied signals may be normal voice or other audio signals or theymay be a variationin-spacing for other purposes such as for directionalindication as shown, for example, in a copending application of EmileLabin and the present inventor, Serial No. 532,724, filed April 26,1944. With such wave trains, the odd and even harmonic content of thepulse train wave varies with avariation in the spacing of the successivepulses. Accordingly, a measure of'the pulse spacing and a consequenttranslation of the signal may be obtained from the amplitudes ofselected odd and even harmonics.

It is an object ofthis invention to provide a translator circuitfortranslating the variation in spacing of pulses of -a pulse train suchasoutlined above. to provide a translation of the signals pro-- ducingthisvariation.

his a further object of my invention to provide a translatorcircuit of atype referred to above wherein a' full l80 rotation of a visualindicator may be readily obtained.-

It is: a still further object of my invention to provide a translationcircuit of the type defined above for reproducing audible signals with agreater linearity than has been provided in'previous forms ofdemodulating translators.

According to a feature of my invention, 1 provide means for selectinganodd'and even harmonic from a wave train of the type defined above, andoutput rectifier means for separately rectifying these selectedharmonics to produce output voltages proportional to the amplitude ofthese harmonics. When a visual meter scale is to beprovided', a separateset of biasing rectifiers is provided together with a common biasing resistor so that the output rectifiers will be biased to an intermediatemid-point. As aconsequence, the output signals will vary betweenpositive and negative values in each of two meter coils so that themeter pointer-may be moved through a 180 arc.

When the circuitis used as a demodulator, aselected odd and evenharmonic is applied across separate rectifier tubes to impedance means;A

reproducer is coupled to this impedance means so that the output willdepend substantially on the sum of the two rectified harmonics thusproducing an output wave of signal frequency having a greater linearitythan if'a-single harmonic selector were used.

A better understanding of my invention and the objects and featuresthereof may be had from the particular description of embodimentsthereof made with reference to the accompanying drawing, in which:

Fig. l is a schematic circuit diagram partly in block form illustratingthe principles of myinvention applied to an indicating meter;

Fig. 2 is a schematic diagram partly in block form illustrating theprinciples of my invention applied to a demodulating receiver; and

Fig. 3 is a'graphical representation illustrating the response obtainedfrom the circuit of Fig. 2.

Turning first to Fig. 1, anincoming wave train A of the type in whichalternate pulses a are spaced substantially, equal distances apart toprovide a substantially constant repetition frequency and in whichsuccessive pulses a, b are spaced apart variable distances in accordancewith the signal, is applied to a receiving antenna I. This energy isreceived in pulse'receiver 2 and detected therein to remove the radiofrequency. The output pulse train is then applied over line 3 and branchlines 4 and -5 to odd harmonic selector 6 and even harmonic selector 1,respectively. The order of harmonic chosen is an inverse function of thepulse displacement and is given by the approximate relation:

where n==Order of harmonic t=Total pulse displacement T-=Base pulseperiod (alternate pulses) harmonics will both be present but ofdifferent amplitudes depending on the departure from the limitingvalues. Accordingly, harmonic selectors 6 and I ar'e'each adjusted to apredetermined one of the odd and even harmonics, respectively.

Output circuits 8 and def selectors B andl, re-

. 3 spectively, are tuned to the corresponding selected harmonic andfeed into tuned translator input circuits I and I I, respectively, whichare grounded at a common point I2. The odd selected harmonic inputcircuit I0 serves to apply this selected harmonic to an output rectifierI3 while the input circuit II applies the selected even harmonic to anoutput rectifier I4. Rectifiers I3 and I4 are provided with anodes I5and I6 and cathodes I1 and I 8, respectively. The output circuit forrectifier I3 includes a cathode resistance I9 which may be shunted by afixed condenser 23 to smooth out the rectified output energy connectedover a lead line 2I and a biasing resistor 22 to common ground point I2.Resistor 22 preferably has sufiicient inherent capacity as indicated bythe dotted line condenser 23 sub stantially to smooth out rectifiedenergy flowing thereover or an actual condenser may be used therein. Theoutput circuit of rectifier I4 comprises a cathode-resistor 24 shuntedby condenser 25, common lead "2| and resistor 22. Across outputimpedances I3 and 24 are connected right angularly arranged meter coils23 and 21 respectively, of indicating meter 28. A permanent magnet 29 isrotatably mounted in the field of coils 26 and 27 so that it will take aresultant position dependent upon the relative strengths of the fieldsof these coils. A pointer 33 cooperative with a calibrated scale 3| ispreferably provided to supply an indication of the relative strengths ofthese fields.

It is clear that with a simple rectified output the currents in coils 26and 2'! would merely vary between zero and some positive value. As acorn sequence, magnet 29 and indicator 30 could then only travel througha 90 indicating are. However, if a negative bias is applied torectifiers I3 and 24, then the currents in coils 2'3 and 21 will varybetween positive and negative values providing a 180 displacement ofpointer 36. order to supply this bias without the necessity ofadditional voltage means and to have this bias value varied inaccordance with the average amplitude of the received energy, I providea rectifier 32 having an anode 33 and a cathode 34 coupled between thejunction point of lines 2i and 22 and the connection to anode I=5 ofoutput rectifier I3 and a similar rectifier 35 provided with an anode 36and a cathode 37 coupled between the junction point of conductor 2I andresistor 22 and the anode of rectifier I4. It Will be noted thatrectifiers 32 and 35 are connected in the opposite direction to outputrectifiers I3 and I4. As a consequence, a substantially uniform voltagedrop will occur in resistor 22 regardless of the variation in amplitudesbetween the selected odd and even harmonics since elements I9 and 24. Itwill be realized that rectifiers I3 and I4 also will tend to provide avoltage drop through resistor 22 which drop would be positive. However,since the output from rectifiers I3 and I4 is applied across resistors I9 and 22, and 24 and 22, respectively, in series, this voltage dropacross resistor 22 will be less than that provided by rectifiers 32 and35. Accordingly, there will be a resultant negative bias voltage appliedacross rectifiers I3 and I4. The relative values of resistors I9, 22 and24 are so chosen that the desired bias is provided for the outputrectifiers I3 and I4. This bias will vary up and down in accordance withthe average energy level of received energy, but will remainsubstantially constant during signal variations. The shift in the zeroaxis, which results due to this bias, is indicated by line 0 of Fig. 3.Therefore, the voltage swing in the coils of meter 2 will be provided toachieve the desired movement of the indicator pointer.

Turning now to Fig. 2, the incoming wave in which the spacing betweenadjacent pulses is varied in accordance with the modulating signals andis applied over antenna I, pulse receiver 2, line 3 and branch lines 4and 5 to odd harmonic selector 6 and even harmonic selector 1,respectively. The outputs of harmonic selectors 6 and I are applied overtuned output circuits 8 and 9 to similarly tuned input circuits I0 andII of the translator circuit 38. A pair of rectifiers 39 and 40 havinganodes 4|, 42 and cathodes 43, 44, respectively, are coupled to inputcircuits In and II. A rectifier output impedance coil 45 grounded at itsmid-point over resistive connector 46 to Coupled to impedance means ofcoil 48 is shown a reproducer An automatic volume control lead 50 isprovided from one end of resistor 46 to pulse receiver 2 to control thelevel of the received signals. automatic volume control is not desired,resistor 46 and lead 50 may be omitted. Condensers indicated by dottedlines are shown connected acros the split transformer windings. Thesecondensers serve a similar purpose as described for condensers 20, 25,of Fig. 1 (i. e. bypassing of the harmonic frequency energy), except inthis case the time constants involved are made sufiiciently small inorder to present suflicient impedance for the demodulated voicefrequency currents.

Turning now to Fig. 3, the operation of the circuit of Fig. 2 will bemore clearly explained. Assuming that the pulse spacing varies along thehorizontal line of Fig. 3 and that at zero the pulses the even harmonicsselected may vary in accordance with curve 5I. Similarly, the amplitudeof the selected odd harmonic will vary in accordance with curve 52, Itis clear, therefore, that from either of these selected harmonics a wavevariable in amplitude in accordance with pulse spacing may be producedin reproducer 49 of Fig. 2. However, by providing the connection asshown in Fig. 2, in which these two output signals are added in opposedphase relationship, the output at reproducer 49 will follow generallythe form shown in curve 53. It will be seen that this curve hassubstantially twice the amplitude swing of either curves 5| or 52 butalso swings through this double amplitude in substantially the same timeas either of these single Waves. As a conselinearity than would bepresent were this simple demodulating circuit used.

It is clear that the simple diagrammatic circuits illustrated are onlytwo of many examples which will readily present themselves to oneskilled in The specific illustration and examples given herein are to beconsidered only by way of and the accompanying claims.

I claim: 1. A translator circuit for cation in accordance withvariations in time dising means for selecting from said pulse trainwaves of a given even and a given odd harmonic of said repetitionfrequency, rectifiers for each of said selected harmonics, input circuitmeans for separately applying said selected harmonics to correspondingones of said rectifiers,- output impedance means for each of saidrectifiers connected to a common point, a common resistor meansconnected between said common point and a common point on said inputcircuit means, and other rectifiers coupled in opposed polarity relationwith respect to said output rectifiers and in shunt relationship to theassociated input circuits and said common resistance to provide abiasing voltage drop in said common resistance for said outputrectifiers.

2. A circuit according to claim 1, further comprising first and secondmeter coils coupled across respective ones of said output impedancemeans, and mounted normal to one another, and a rotatab-ly mountedmagnet indicator mounted in the common fields of said meter coils.

3. A translator circuit for reproducing a signal from a received pulsetrain in which the time spacing between adjacent pulses varies inaccordance with signals and the alternate pulses of said train havesubstantially constant repetition frequency, comprising means forselecting from said pulse train waves of a given even and a given oddharmonic of said repetition frequency, rectifiers for each oi saidselected harmonics, an output impedance means connected between saidrectifiers, a ground connection to the mid-point of said outputimpedance means, and a signal reproducing means coupled to said outputimpedance means.

4'.- A circuit according to claim 3, further comprising a resistancemeans in said ground connection across which a substantially constantvoltage dependent upon the received signal is produced, and volumecontrol means for said translator circuit controlled by saidsubstantially constant voltage.

ing amplitude, separate 5. A translator circuit for translatingindicating signals comprising component waves varying in relativeamplitude in accordance with different indications, comprising means forselecting from said signal waves said component waves of varyrectifiermeans having output circuits for rectifying said separated vnaves,common resistor means in the output circuits of said rectifiers, atranslator coupled to receive the output energy of said rectifier meansfor producing a translation of said signals, and means for utilizing thepotential drop in said common resistor to control said translatorcircuit.

6. A translator circuit for indicating signals comprising componentWaves varying in relative amplitude in accordance with difierentindications, comprising means for selecting from said signal wavescomponents of said varying amplitude, separate rectifier means forrectifying said separate components, output circuits for said rectifiermeans comprising an inductance coil coupled between said rectifiers andresistor means for grounding the midpoint of said coil, and an audiosignal reproducing means coupled to said coil for producing a.translation of said signals.

'7. A translator circuit for translating indicating signals, comprisingcomponent waves varying in relative amplitude in accordance withdifferent indications comprising means for selecting from said signalwave component waves of varying amplitude, separate rectifier meanshaving output circuits for rectifying said separated waves, biasingmeans for said rectifiers comprising a common resistor in the outputcircuits of said rectifier means, and other rectifier means connectedacross the input of said first-named rectifier means to produce abiasing drop in said common resistor, and a translator coupled toreceive the output energy of said first-named rectifier means forproducing a translation of said signals.

DONALD D. GRIEG.

